Humidistat



J. W. KEENAN HUMIDISTAT 2 Sheets-Sheet 1 Filed May 7. 1954 m m H i m 8 a M U M w W K. A L A W Y S V e i m. L

z u n Feb. 5, 1957 J. w. KEENAN 2,780,687

HUMIDISTAT Filed May 7, 1954 2 SheetsSheet 2 Fig.2. FLO. 3. 27

1 N VENTOR James W Keercam ATTORNEY United States Patent 6 is HUMEDISTAT James W. Keenan, Baltimore, Md., assignor to Bendix Aviation Corporation, Baltimore, Md., a corporation of Delaware Application May 7, 1954, Serial No. 428,319

7 Claims. (Cl. 20061.06)

This invention relates to a device for controlling the operation of a machine or apparatus effective to maintain the moisture content of the air within a prescribed enclosure at a predetermined value, such device being commonly known as a humidistat.

An object of the invention is to provide a humidistat capable of meeting the growing demand for a device of this kind which is simple in construction, low in cost of manufacture, and which at the same time is reliable and relatively accurate in operation.

Another object is to provide a device of the type specified employing hair strands as the sensing element and associated switch control and adjusting .or setting means of an extremely simple yet elfective nature, the strands being so connected at their free ends and the associated parts being so designed as to facilitate mass production and greatly simplify servicing and maintenance.

A further object is to provide a simple, low-cost humidistat which will eifectively make and break an associated electric control circuit in response to changes in humidity without requiring interconnected relays or like devices.

The foregoing and other objects and advantages will become apparent in view of the following description taken in conjunction with the drawings, wherein:

Fig. l is a view in elevation of a humidity controller or humidistat in accordance with the invention, having the cover thereof removed and part of the switch assembly housing broken away;

Fig. 2 is a bottom view in edge elevation of Fig. 1, with part of the casing broken away;

Fig. 3 is a section taken on the line 33 of Fig. 1; and

Fig. 4 is a section taken on the line 44 of Fig. 3.

Referring to the drawings in detail, the parts of the humidistat are supported by a mounting bracket shown in the form of a case-half, generally indicated at 10, which may be made of pressed sheet metal or other suitable material, said bracket having a back wall 11 and end walls 11 and 11". The wall 11 is formed with key slots 12. by means of which the device may behung on headed screws or like elements anchored in a wall or other convenient support. An open-mesh ventilated cover 13 is provided with lugs 13' for snap-on engagement with top and bottom flanges 14 and 15, formed integral with the back wall 11. A sensing element comprises a cable 16 made up of strands of material, preferably human hair, responsive to changes in humidity, the strands being of suitable length and trimmed at their free ends for insertion in the shanks 17" ofterminals 17 and 17'. These terminals may be stamped from sheet metal with the shanks initially open to receive the free ends of the strands and thereafter bent over and pressed down in clamping engagement with said ends.

A pulley wheel 18 is journaled on-a bearing pin 19, carried by the forked end of a channel-shaped lever 20,

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which may be formed of sheet metal such as spring steel, the opposite end of said lever being riveted to an outwardlybent portion 21 of a bracket 21, secured by a rivet 22 to the back wall 11. The free end of the bracket 21 is bent over and anchored in an opening 23, punched out of said side wall.

The lever 20 is sprung into abutting engagement with the free end of a setting or adjusting screw 24, threaded through a bushing 25, secured to the adjacent end wall 11", the said screw 24 having a shank or stem 25 projecting outwardly therefrom, on which is removably inserted a knob 27. By turning the screw 24, the effective position of the lever 20 may be adjusted, to thereby place the hair strands 16 under proper tension.

The terminal 17 of the cable or strands 16 is engaged over a hook-on finger 28', struck up from one end of a switch lever 28, the opposite end of the said lever terminating in a foot 28", connected to the one extremity of a leaf spring 29, the latter having its lower end connected to the bent-over portion 38 of a supporting bracket 33 by rivets 31. Preferably, the spring 29 has a localized flexing area provided by reducing the thickness of the spring in said area. in the present instance this is done by forming laterally-aligned edge and central notches the spring as indicated at 2.9, Fig. 4. The bracket 3% is anchored, as by riveting, to the back wall 11. The foot 23 is in operative dcpressing engagement with a switch plunger or contactactuator 32 (Fig. 1), normally urged toward break position by a snap-action terminal-bridging spring strip 33. The strip 33 has a bowed stressed spring portion 33, which is in engagement with the contiguous end of the plunger 32; and at its upper end said strip carries a contact 34. The lower end of the spring strip 33 is anchored to a terminal 35. At one side of the contact member 34 is a stop 35, and to the right of the free or contact-carrying end of the spring 33 is a mating contact 35, formed on a terminal 40', note Fig. 2. The plunger 32, spring 33, terminals 35 and 4G, stop 35 and contact 35 constitute part of a switch assembly which is mounted in a casing 35, provided with an insulation cover 36, said casing being anchored to the back wall 11 by means of screw bolts 37, having screw-threaded ends projecting through spring fingers 38 punched outwardly from an elongated fiat twin-type speed nut 38. This type of nut may be made of a strip of sheet metal and facilitates assembly, since it need only be pressed over the threaded ends of the bolts before the latter are tightened down. Terminal wires 39 and 49 are brought out from the terminals 35 and 40' and constitute a connecting cable 41, leading to a suitable plug 42, adapted for connection to a source of potential, usually a volt supply. The plug is of that type having sockets 42' in its outwardly facing end, to accommodate an electrical connection to the humidifying or dehumidifying machine or apparatus, not shown.

The spring 29 provides a pivotal mounting for the foot 23" of the switch lever 23, and it also functions as a means for biasing the lever 28 to a predetermined position, and it will do this irrespective of whether or not the switch plunger 32 is spring-biased to return position. Since the spring 2? biases the lever 23 to a given switch position, the switch lever 28 will work equally well with a switch having a contact-actuating member or plunger of the spring-return type such as that shown, or one having an actuator which requires a positive connection to the lever 23 to effect movement of the actuator to make and break positions. Also, when the humidity element or cable 16 is removed, the switch lever 23 will return to and remain in its predetermined or preset position.

Operation As is wellknown by those versedtin theart, the hair strands cable 16 will contract when dry and expand when Wet. In the type of installation shown in the drawings, the humidistat is adapted to startand stop dehumidifying apparatus. .In other words, when the air within'the enclosure to be controlled attains a degree of relative humidity greater than a predetermined setting of the humidistat, the control switch is thrown into a make position to start the dehumidifying apparatus. In the position of the switch elements as shown in Fig. l, the humidity element orcable 16 is extended, due to increased humidity, to a point where the foot 28 of lever ZShas been moved to the left by the bowed spring 33 of the bridging strip 33,.causing the contact 34 to snap to its closed position. Should the air dry out to a point beyond the setting of the humidistat, the element 16 will contract, rotating the lever 28 in a clockwise direction and depressing the plunger 32. When the plunger 32 has been depressed to a point where it moves the spring 33 just past dead center, the free end of the strip 33 will flex to the left and snap the contact 34 against stop 35', whereupon the dehumidifying apparatus will be stopped and will not restart until the air has again attained the required degree of relative humidity.

The majority of parts may be made from simple sheet metal stampings and easily and quickly assembled in the casing Id. The tensioning spring 20, pulley 18 and bracket 21 may be separately fabricated and easily and quickly installed as a unit, with the proper location spotted by the hole 23 and rivet hole for rivet 21. Likewise the bracket 28, leaf spring 29 and bracket may be preassembled and installed as a unit. This being done, it is only necessary to string the strands 16 over the pulley and attach the terminals 17 and 17' to their hooks 2S and 34. Also, the switch assembly may be separately assembled and secured as a unit to the back wall 11 by the bolts 37 and speed nut 33.

Should the apparatus to be controlled act to humidify the air, then the contact need only be so located as to be engaged by contact 34 when cable 16 contracts as a result of drying or dehumidification of the air in aroom or enclosure. Again, should both humidifying and dehumidifying apparatus be under control of the humidistat, then the switch assembly should incorporate a suitable arrangement of contacts, for example, contacts located on opposite sides of a snap-action bridging strip having a neutral or dead-center position, subject to being thrown into bridging position by expansion and contraction of the cable 16.

It will be understood that limited changes in construction and arrangement of the parts of the humidistat as illustrated and described herein may be made to adapt the same to difierent installations within the scope of the appended claims.

What is claimed and desired to be secured by United States Letters Patent is:

l. A humidistat comprising a casing, an adjusting screw rotatably supported in the wall of said casing and having one end projecting into the interior of the casing, a humidity responsive element consisting of a cable of humidity-responsive material having hook-on terminals secured to the free ends thereof, a pulley or roller over which said cable is trained, a spring biased lever rotatably supporting said pulley or roller at its one end, means supporting the opposite end of said spring biased lever from said casing in a manner such as to cause said lever to resiliently abut the free end of said screw, an electric switch having a plunger depressible against the biasing force of a return spring, a Iockable switch lever for depressing said plunger having a leaf spring connected to one end thereof and effective to bias the lever to a predetermined position, one end of said cable being connected through its associated terminal to said switch lever and the opposite end of the cable being anchored through cable contracts the switch lever is rocked or rotated against the "force "of its biasing spring to 'depress said plunger.

2. A humidistat comprising an elongated casing including a mounting plate, an adjusting screw rotatably supported in a wall of said plate and carrying a knob on its outer end exteriorly of said Wall and having its opposite or inner end projecting into the interior of the casing, a humidity responsive element consisting of a cable of humidity-responsive material having hook-on terminals secured to the free :ends thereof, a pulley 'or roller over which said cable is trained, a lever having a forked end rotatably supporting said pulley and a springbiased portion at its opposite end which'is supported from said casing in a manner such as'tonormally urge said lever against the inner end of said screw, an electric switch having a depressible plunger spring-biased to return position, a leaf spring having one end anchored to said casing and itsopposite-end projecting free adjacent saidplunger, a switch-lever havingoneend connected to the'free'end of said spring and a terminal hookatits opposite end, oneof said hook on'terminals being engaged with said hook and the-other of said 'terminals being anchored to said plate.

3. A hum-idistat comprising a casing, an adjusting-screw rotatablymountedin a wall of said casing andhaving a manually adjustable member at its one end accessible exteriorly of said casing, the opposite end ofsaid screw projecting free interiorly of said casing, a pulley'or'roller, a spring-biased channel-shaped lever having "a fork *a't'its oneend rotatably supporting'said pulleyor-roller, means supporting 'the opposite end of said pulley-supporting lever from said casing in a predetermined position in which said --pulley-supporting lever is resiliently urged into abutting engagementwith'thefree end of said'screw, a depressible plunger constituting part of an electric switch assembly, a leaf-spring having its one end anchored to said casing and at its opposite-end projecting free adjacerit said plunger, a switch lever fixed at one end to said leaf spring and having a-hook-on member atits opposite end, said switch assembly also including a pair of-spaced terminals and a resilient bridging element fixed at one end and carrying a contact at its opposite end, said bridging element being provided with a stressed'spring'memberin engagement with-one end of said plunger, a humidity responsive element=consisting of a plurality of strands of hair having hook-on terminals secured to the free ends thereof, said strands being trained -.over said pulley or roller and having one of said hook-on tenninals engaged over said hook and the other of said ho'ok-on terminals anchored tosaid casing, rocking movement of said switch lever through a'predetermined arc-depressing said plunger to a point where it causes said stressed spring member to snap said bridging element to make or break position.

4. .A humidistat as claimed in claim 3, wherein said leaf-spring has a localized flexing area.

5. A humidistat comprising a casing, an adjusting screw rotatably mounted in a wall of said casing and having a free end projecting into the .interior of the casing, a humidity-responisve element consisting of a plurality of strands of humidity-responsive material ar' ranged in the form of a cable and having hook-0n terminals secured to the free ends of the cable, a single roller or pulley wheel over which said cable is trained, a spring-biased member rotatably supporting said roller at its one end, means supporting the opposite end of said. member from said casing in a manner such as to resiliently urge .said member against the free end of said adjusting screw, an electric switch assembly including a contact-actuating element, a switch lever having a rockable fo'ot portion at its one end for actuating said contact-actuating element and a terminal hook at its opposite end, means anchoring said foot portion to said casing including a leaf-spring member which biases said foot portion to a predetermined position, one end of said cable being connected to said hook and the other end thereof being anchored to said casing.

6. A humidistat comprising a casing, an adjusting screw rotatably mounted in a wall of said casing and having a free end projecting into the interior of the casing, a plurality of strands of humidity-responsive material, a spring-biased member having one end projecting free and its opposite end supported from said casing in a manner such as to resiliently urge said member against the free end of said adjusting screw, an electric switch assembly including a contact-actuating element, a switch lever having a rockable foot portion at its one end for actuating said contact-actuating element and its opposite end projecting free, said strands being connected to and extending between the free ends of said member and said lever, and means anchoring said foot portion to said casing comprising a leaf-spring member which biases said foot portion to a predetermined position.

'7. A humidistat comprising a casing, a set screw adjustably threaded through a wall of said casing and having a free end projecting into the interior of the casing, a length of humidity-responsive material having hook-on terminals secured to the free ends thereof, a member formed at least in part of leaf-spring material having its one end projecting tree and its opposite end anchored to said wall in a predetermined position in which said member is resiliently urged into abutting engagement with the free end of said screw, an electric switch assembly including a spring-return contact-actuating plunger, a switch lever having a foot portion at its one end for depressing said contact-actuating plunger against its spring and a terminal hook at its opposite end, means pivotally supporting said lever with said foot portion in operative relation to said plunger, spring means normally urging said foot portion to a predetermined position with respect to said plunger, said length of humidity-responsive material being connected to the free ends of said switch lever and said member and normally held under tension therebetween.

References Cited in the file of this patent UNITED STATES PATENTS 1,995,430 Lewis Mar. 26, 1935 2,468,673 Kaminsky Apr. 26, 1949 2,573,588 Miller Oct. 30, 1951 

